That’s because the car tests were utterly unrepresentative of the operating conditions for cars…and made even more so by one manufacturer who twigged that it was only necessary to conform to the test parameters when the non-driven wheels of the car weren’t turning…because that meant it was on a test rig!
The truck/bus tests are more realistic by far. And Euro VI heavy-duty diesels actually monitor the gases going in and out of the SCR box in the exhaust and adjust the AdBlue dose in real time to ensure conformity.